MPEG (Motion Pictures Experts Group) was an outgrowth of earlier standards work for digital compression of still pictures. The international MPEG committee started in 1988 with the goal of standardizing video and audio for compact discs. The compression work for MPEG-1 was based upon film or other progressive sources. By 1990 the MPEG committee had created a data structure syntax for Source Input Format (SIF) video and compact disc audio using a combined data rate of 1.5 Mbit/Sec. This system approximated the perceptual quality of VHS consumer video tape, making MPEG video compression a visually acceptable technology. Although this MPEG standard was viable for progressive sources like film, it lacked the techniques to deal with standard broadcast interlaced video with good compression.
In 1992 over 200 companies from around the world were involved in the MPEG-2 draft development, demonstrating strong support for the technology specification. Today, MPEG-2 syntax has been adopted for the United States Grand Alliance High Definition Television (HDTV) specification, the European Digital Video Broadcasting Group, and for the high density compact disc. MPEG 2 and MPEG 2 "near compliant" is also the backbone of commercially operational Direct Broadcast Satellite (DBS) systems like DirecTV or USSB. MPEG encoded video offers broadcasters the ability to transmit more programs on a given transmission channel. This means more channels at a lower infrastructure cost. In addition, digitally encoded streams eliminate drift, remove certain kinds of analog distortion, and reduce system wide maintenance.
MPEG is, generically, a means of compactly representing digital video and audio signals for consumer distribution. The basic idea is to transform a stream of discrete samples into a bitstream of tokens which takes less space, but is just as filling to the eye or ear. This "transformation" exploits perceptual and even some actual statistical redundancies.
MPEG currently consists of two operating specifications, MPEG 1 and MPEG 2. MPEG 1 was developed for progressive source materials like film, while MPEG 2 was enhanced to address the interlaced materials common in broadcast TV. Both standards include video, audio, and systems components such as time stamping for synchronization. The orthogonal dimensions of Video and Audio streams can be further linked with the Systems layer--MPEG's own means of keeping the data types synchronized and multiplexed in a common serial bitstream.
The essence of MPEG is its syntax: the little tokens that make up the bitstream. MPEG's semantics tell a decoder how to transform the compact tokens back into something resembling the original stream of samples. These semantics are merely a collection of agreed-upon rules which are highly reactive to combinations of bitstream elements set in headers and so forth.
The Digital Video Broadcasting (DVB) group has specified a framing structure for the QAM/QPSK transmission of MPEG-2 transport stream packets in its ETS standard. Each frame consists of a frame header packet that includes a byte with hexadecimal value "b8" (hereinafter abbreviated "0.times.b8") in the packet sync position and 7 additional transport stream packets with the hexadecimal byte "47" (hereinafter abbreviated "0.times.47") in their packet sync positions. Each of these transport stream packets is comprised of 204 bytes of data with sync byte being the first byte of the packet. Depending on the modulation scheme, the data frame is subdivided into fixed length symbols prior to transmission. At the receiving end these symbols are recovered through, for example, an equalizer or trellis decoder, or a combination of both.
There are two prior art implementations for detecting the Sync pattern which is obtained from literature:
1. Adder Tree Method, and PA0 2. Implementation with ROMs
In a conventional synchronization circuit a circular buffer of size 1632 bits (one frame=204 bytes times 8 bits per byte) can be used to detect the repetitiveness of the sync pattern. Additionally one needs to track the occurrence of 7 or less sync patterns between two consecutive frame header patterns. Such an implementation is typically hardware intensive.